(IDEX Online) - A Cartier ring featuring a huge 21.86-carat Colombian emerald sold for $3.65m, almost four times the high estimate of $1m by Sotheby's New York.It was the headline lot in a sale of the "very complete jewelry wardrobe" collected by the late philanthropist and society hostess Cecile Zilkha.The square emerald-cut stone (pictured) was described as "richly saturated medium deep slightly bluish green, slightly included with a few surface reaching inclusions".It was set in gold, flanked by baguette and single-cut diamonds weighing a total of 1.45 carats.The estimate for the ring, at last week's Magnificent Jewels sale, was $750,000 to ?, ?1m.Mrs Zilkha, wife of the Iraq-born financier Ezra Zilkha (who died last year), was an accomplished jewlery connoisseur. Her collection included contemporary commissions by Cartier, Van Cleef & Arpels, Bulgari, and Harry Winston, as well as period pieces of noble provenance. She often hosted Ronald Reagan, Anwar Sadat, David Rockefeller, Henry Kissinger and other close friends at the couple's Fifth Avenue apartment.